As you’ve seen already in this chapter, Messages lets you share your thoughts, your voice, and your image with the people on your buddy list. And now, for its next trick, it lets you share…your computer.

Messages’s screen-sharing feature is a close relative of the network screen-sharing feature described in Chapter 14. It lets you not only see what’s on a faraway buddy’s screen, but also control it, taking command of the distant mouse and keyboard. (You can share your screen with the other guy, too.)

You can open folders, create and edit documents, and copy files on the shared Mac screen. Sharing a screen makes collaborating as easy as working side by side around the same Mac, except now you can be sitting in San Francisco while your buddy is banging it out in Boston.

And if you’re the family tech-support specialist—but the family lives all over the country—screen sharing makes troubleshooting a heckuva lot easier. You can now jump on your Mom’s shared Mac and figure out why the formatting went wacky in her Word document, without her having to attempt to explain it to you over the phone. (“And then the little thingy disappeared and the doohickey got scrambled…”)

To make Messages screen sharing work, you and your buddy must both be running Macs with OS X 10.5 (Leopard) or later. On the other hand, you can share over any account type: AIM, iCloud, Google Talk, Yahoo, Jabber, or Bonjour.

To begin, click the sharee’s name in your buddy list.

Once the invitation is accepted, the sharing begins, as shown in Figure 12-25. To help you communicate further, Messages politely opens up an audio chat with your buddy so you can have a hands-free discussion about what you’re doing on the shared machine.

Figure 12-25. Top: You either send or receive an invitation to start sharing your screen, but make sure you know with whom you’re dealing before accepting the offer and starting the sharing process. Bottom: When you’re sharing someone else’s screen, you have the option to click back and forth between the two Mac screens.

If you’re seeing someone else’s screen, you see his Mac desktop in full-screen view, right on your own machine. You also see a small window showing your own Mac; click it to switch back to your own desktop.

To bail out, press Control-Esc on the Mac’s keyboard.